HVAC systems typically include an air handling unit (AHU) configured to provide fresh air to a facility via associated air ducts, and to remove air from the facility, thereby providing fresh air circulation. On the supply side, the AHU includes a heat exchange coil and a control valve, along with a supply air fan (SAF). The SAF pushes air across the coil and through a primary air (PA) casing, and to the facility. On the return side, the AHU includes a heat pump and a return air fan (RAF), which induces air to move from the facility to an exhaust. A heat recovery wheel may intersect both the return and supply sides and may cool and/or dehumidify the inlet air.
Some HVAC systems also include one or more chilled beams (CB). CBs are pipes or other structures filled with a chilled cooling medium, such as water, which courses therethrough. The CBs are typically hung from the ceiling of the facility, and supply air pushed from the AHU by the SAF is routed past the CBs by a CB fan. The CB fan speed and/or power state may be modulated to control the air temperature and/or CO2 level in specific areas of the facility.
The SAF speed and supply air temperature (SAT) are typically controlled by comparing the pressure and temperature, respectively, in the PA casing to setpoints. The RAF control is linked to the SAF control, such that the RAF is configured to provide a percentage (e.g., 80%) of the volumetric flow rate produced by the SAF. The CB fan speed, on the other hand, is controlled by comparing the temperature and/or CO2 level in the facility to setpoints, to maintain a desired temperature and avoid excessive CO2 levels.
The SAF and CB fan controllers are typically controlled separately, at least from a conceptual standpoint, and often through separate hardware. However, the pressure in the PA casing often varies even when the CB fans are operating under reduced load, or are not on at all, for example, through natural ventilation. Accordingly, even when not required by the facility air temperature or CO2 levels, the SAF (and thus RAF) continue to run for longer and/or at higher speeds than necessary, in an attempt to maintain the pressure in the PA casing at the setpoint.
What is needed is an apparatus and method for coordinating control of the SAF and CB fan to avoid unnecessary running of the SAF and/or RAF.